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Optical reference cavities are a key component of ultra-stable lasers. Based on the theory of elastic deformation, the displacement difference between the top and bottom mirrors of an optical vertical cavity supported on the midplane was analyzed in the present research. The displacements and tilt angles of the two mirrors of the optical reference cavity were deduced based on Poisson’s ratio. In order to verify the validity of the theoretical analysis, the vibration sensitivity induced by the elastic deformation of vertical optical reference cavities was simulated by finite element analysis. In order to compensate for the displacement difference between the top and bottom mirrors under an external force, the zero vibration sensitivity of the optical cavities was achieved by changing the thicknesses of Ultra-Low Expansion glass rings and the mirrors. The results and methods presented in the present paper may facilitate the design of vertical reference cavities, especially transportable optical reference cavities.

We extend the array theory to design 2D curved coding metasurfaces in order to achieve arbitrary wavefront control. The extended array theory establishes the relationship between wavefront and curved-surface, which provides a simple and effective method to obtain the layout of desired metasurfaces. According the theory, we present 2D curved metasurfaces with 3-bit coding elements. Both simulations and measurements demonstrate that the proposed designs can manipulate wavefront effectively. For normal incidence, the aperture efficiency of normal reflection is more than 90%. For general oblique incidence, the proposed designs almost meet the expectances, but the aperture efficiency decreases with the increase of desired scattering elevation angle. The curved coding metasurfaces are expected to be applied to many devices such as conformal antenna array.

The ultra-stable laser is significant in optical atom clock. The frequency stability of the laser is limited by the thermal noise of the cavity, which can be reduced by using the long cavity. In this paper, we demonstrate an ultra-stable laser system at NTSC that stabilized to a 30-cm-long optical reference cavity at 698nm, the calculated thermal-noise-limited of frequency stability is around $1 \times 10^{-16}$. We evaluated the influence of major noises and the results show the Allan variance corresponding to all these noises can be reduced to the fractional frequency stability of less than $6 \times 10^{16}$ at one second.

Aiming at the problem of the fracture of the swing arm of a heavy-duty tow and hang separation type of wrecker, an improved design scheme for the reinforcement of the basic arm and swing arm beam structure is proposed. The finite element model of the arm bracket structure before and after the improvement was established, and the three working conditions of full shrinkage, semi-extension and full extension were selected. The maximum lift weight under different amplitude angles was selected as typical working conditions for checking calculation. On this basis, a comparative analysis of the structural strength of the arm bracket is carried out. The results show that the maximum stress of the arm bracket is reduced by 27.86 MPa after the improvement, and the stress distribution of some components is obviously improved.

We report the development of ultrastable lasers at 1.5μm. Through PDH method, the fiber lasers are locked to two ultra-stable optical cavities with finesse of 483000 and 148000 respectively. Through comparing two similar ultrastable laser systems, the linewidth of 0.68Hz and the fractional frequency instability of 2.7×10-15 at 1s averaging time are achieved.

In this paper, a high-efficiency and wideband converter based on a petal metasurface is proposed. This polarization converter can convert the linearly polarized incident electromagnetic wave to its orthogonal counterpart upon the reflection mode at resonance frequencies of 7.55 GHz, 14.15 GHz, 22.23 GHz, and at these three frequencies, the cross-polarization coefficient is almost 100%. The efficiency of the converter is higher than 90% from 6.81 GHz to 23.03 GHz. Moreover, its parameters of periodic and thickness are tunable. The physical mechanism is revealed by further analysis. Such a scheme of the linear polarization converter has potential applications in microwave communications, remote sensing, and imaging.

The National Time Service Centre of China is developing a 698 nm ultra-stable clock laser system for dedicated use in a space strontium optical clock. This report present the development of this system. The laser reaches a frequency instability of $3.5 \times 10 ^{-15}$ at 1 s averaging time and the linewidth is about 1.3 Hz.

The structural learning is the core of the Bayesian network learning. The study of Bayesian network structure from the sample data is NP-Hard problems, and the current mainstream approach is to combine the heuristic algorithm. The paper uses multi-population bacteria foraging optimization (MBFO) algorithm to study Bayesian network structural learning,. Finally, the algorithm is proved to be more effective in the standard Bayesian network Cancer network, Asia network, Car network than classical structural learning algorithm.

Communication signal modulation recognition refers to a process of automatically processing a received signal and determining its modulation type. As an intermediate part of signal detection and demodulation, modulation recognition technology plays an important role in a variety of civilian and military applications such as cognitive radio, electronic reconnaissance, and intelligent demodulator. After several decades of development, modulation recognition technology has made many achievements. However, with the increasing demand for engineering and the increasingly complex wireless communication channel environment, there are still many issues to be solved. This paper presents a method of deep learning for modulation recognition. Deep learning allows for automatically learn features directly from simple wireless signal representations, without the need to design of hand-crafted expert features such as high-order cyclic moments. The neural network used in this paper is the deep belief network. Experimental result shows that using the temporal IQ data representation to recognize modulation formats contributes to the high correct recognition rate at high SNR. When the SNR is $18\mathrm {d}\mathrm {B}$, the average recognition rate still reaches 92.12%.

The mass vibration sensitivities are calculated by using FEA under a variety of variables including cavity's length and supporting position. The calculation results show that the effect of ULE rings on the vibration sensitivity is greater with increasing the cavity's length in the case of other variables unchanged. For longer cavities, as the distance between supporting position and ULE rings increases, the length variation induced by ULE rings is obvious, eventually leading to change the position of zero vibration sensitivity. In conclusion, the analysis results about the effect of ULE rings on the vibration sensitivity in this paper are helpful to optimization design of vibration sensitivity of horizontal ultra-stable optical reference cavities, specifically longer and thinner optical reference cavities.

We propose the design and simulation of a dual-band reflective polarization converter in the microwave region based on multiple resonances. An ultra-thin broadband polarization conversion composing of arrays of electric-field-coupled (ELC) resonator, a dielectric layer and a continuous metallic layer is further demonstrated numerically. The proposed converter can rotate the linearly polarized (LP) waves to its cross-polarized ones at resonant frequencies of 8.9 GHz and 14.8 GHz. Also, it can convert LP waves to circularly polarized waves at other two frequencies. The simulated results demonstrate that the bandwidth of polarization conversion ratio (PCR) over 50% can be achieved from 8.2 GHz to 16.7 GHz. And the maximum polarization conversion efficiency is nearly 100% at the two resonant frequencies. What's more, the proposed converter can maintain the polarization conversion performance with incident angle up to 30°.

The aperture integral equation (AIE) and method of moment (MoM) technique is proposed for analyzing the electromagnetic scattering properties of a finite perfectly conducting cone loaded with a slot. The solution allows us to deal accurately with slots of any shape. Two kinds of slots representing for electrical large and electrical small structure respectively, are considered in this paper. Bi-static radar cross sections (RCS) of the slotted cone and near field scattering at slot aperture are discussed for the incidence plane wave located near the axial direction. Numerical results are presented and demonstrated the slot apertures whether electrical large size or electrical small size can be significantly improved to increase electromagnetic scattering of the considered finite cone in certain direction. Moreover, grooved conducting cone are also treated as a special case, and its electromagnetic scattering properties are compared to the slotted ones.

Vibration-insensitive spherical optical reference cavities are important to ultra-stable lasers. Striving for even lower instabilities of ultra-stable lasers, it is essential to study the stiffness analysis of vibration-insensitive optical reference cavities. Theoretically, under the other same conditions, greater stiffness could lead to lower vibration sensitivity and Brownian thermal noise. In this paper, the stiffness of a spherical optical cavity mounted at two support points on a diameter of the spherical spacer are analyzed theoretically. The analysis results show that the maximum values of the three kinds stiffness and bending shearing force are located in the support point of the cavity. Additionally, the minimum of that and the maximum of axial stress present to radius of the cavity. On the whole, five function curves of the stiffness and two key forces are nonlinear as a function of the length of the optical axis. The analysis results in this paper are helpful to optimization design thermal noise and vibration sensitivity of spherical optical reference cavities.

In the process of highway operation, huge energy consumption occurs and a lot of pollutant will be emitted. To get an intuitive impression on spatial and temporal distribution of energy consumption and emissions, an energy consumption and emissions accounting model based on multiple sensors are provided, which can be used for detection, analysis and management of energy consumption and pollutant emission. In this model, energy consumption and emissions experimental data from different vehicle type, highway operation and maintenance data are included. The output of the provided model can be used as basic data for highway energy-saving, emission reduction and green highway grade evaluation. Finally, some suggestions are summarized which are based on the key factor analysis in the model construction process.

Thermal noise in optical cavities sets a fundamental limit to the frequency instability of ultra-stable lasers. We estimate the contribution of the sphere spacer using the new Equation based on Levin's formulation of the fluctuation-dissipation-theorem (FDT) and elastic strain energy. Focusing on the sphere spacer geometry, the estimate and simulation of the thermal noise have been carried out. We find that thermal noise of the sphere spacer behaves different from cylindrical cavities. The estimate for the sphere spacer by the new Equation agrees better with simulation compared with previous equations.

Thermal noise in optical reference cavities sets a severe limit to the frequency instability of ultra-stable lasers. We, for the first time, give an analytic expression of the contribution of the spindle spacer based on Levin's formulation of the fluctuation-dissipation-theorem (FDT). The analysis indicates that the thermal noise of spindle cavity has a few different features from cylindrical cavities with similar geometry. The analytic estimate for the spindle spacer by our equation fits better with finite element analysis (FEA) results compared with previous equations.

Along with the rapid development of the optical clocks, optical frequency transfer via communication fibers has shown much higher precision than the conventional methods. In this paper, we report the progress on the optical frequency transfer via communication fibers at NTSC. Over a 71-km spooled fiber, the optical frequency transfer with a residual instability (Allan deviation) of 5.4E-15 at 1s and 5.6E-18 at 10 4 s is demonstrated. Furthermore, for a measurement bandwidth of 100 Hz, the instability is 1.2E-15 at one second and 1.4E-18 at 10 4 s. This transfer instability is fundamentally limited by the fiber length. The Allan deviation curves fall as τ -1 for short times, which is consistent with the fact that the transferred signal is dominated by white phase noise. This experimental achievement provides the foundation for the upcoming optical transfer experiment over a 300-km urban communication fiber link.

Foreground detection, which directly affects the performance of the following target tracking, object recognition and behavior analysis process, is very important for video surveillance. Recently, Independent Component Analysis (ICA) based foreground detection strategies have been proposed. However, the matter of uneven change of illumination is not well handled in the existing methods. In this paper, we propose a simple and efficient spatial pyramid strategy based on ICA, which is robust to uneven illumination changes. Concretely, we partition the video frames into suitable number of subregions and apply Contextual Constrained Independent Component Analysis technique inside each subregion. Two set of video frames involving room lights turn on/off and room door open/closed are selected in the training and test process. The experiment results demonstrate the improvement of our strategy compared with the temporal differencing, basic ICA model and the Contextual Constrained Independent Component Analysis strategy.

With huge amount of visual data being online, the need for automatic illegal images filtering system becomes increasingly urgent. A key ingredient in the design of such systems is the asymmetric image classification module. Among the proposed strategies, bag-of-features models together with kernel based classifiers have demonstrated impressive performance. However, when dealing with this asymmetric learning problem, their efficiency is often impaired. This may own to the fact that, a universal codebook is not adequate enough to deal with this kind of problem, which make the classification task difficult. This article proposes a novel approach, where a cascade codebook with a sequence of node codebooks is used to represent images. The experimental results show that, this novel strategy outperforms the approaches which use only one universal codebook.

This paper proposes a modified two-class LDA based compound distance for similar handwritten Chinese characters discrimination. First the definition of the Intersecting Subspace (IS) between two classes and the modified between-class scatter matrix is given. Then we prove that the modified between-class scatter matrix can supply additional information. Our experiments demonstrate that the additional information can be used to discriminate points in the IS and the proposed method outperforms the previous LDA based method.

An important consideration in designing of visual object classification systems is the representation of images. In the past decades, significant improvement has been made, which can owe to two strategies: the proposal of new discriminative local image features together with the combination of existing local image features. In this paper, several strategies which provide the combination weights of different local features are enumerated, and then our own strategy, in which the weights of multiple features are determined by their contributions to the classification performance, is proposed. At the end of the paper, we provide our result in Visual Object Classes Challenge 2009 (VOC 2009), which shows that the strategy is competitive with state-of-the-art methods while the processing time is dramatically reduced.

Ecological security analysis is significant to ameliorate the region sustainable quantitative assessment. Based on the principle of ecological footprint, Ecological security in Liaoning coastal economic zone is studied in this paper with three indexes, which are ecological tension index, ecological occupancy index and ecological economic coordination index. The results show that the ecological load exceeds the capacity in Liaoning coastal economic zone, and existing development model is not sustainable. The change trend of ETI is increased firstly and then decreased.

Land use and land cover change (LUCC) is an important factor of global environmental change. LUCC model is the focus of land change research. LUCC of the study area in the next 13 years is predicted based on CLUE-S model. Two prediction scenarios were used which are with or without considering “Liaoning Coastal Economy Development Plan”. The results showed that the construction land increased dramatically from 1988 to 2007 due to the economic, population growth and urbanization speed up, while farm, water and forest land decreased correspondingly. At the same time, Landscape fragmentation in the study area accompanied these changes. Landscape change trends under the two prediction scenarios plan are similar. However construction land expanded and farm land decreased more dramatically under the planning scenarios. The regional development model is not sustainable.

We report our work on evaluating performance of several MPI Allgather algorithms on fast Ethernet. These algorithms are ring, recursive doubling, Bruck, and neighbor exchange. The first three algorithms are widely used today. The neighbor exchange algorithm which was proposed by the authors incorporates pair-wise exchange, and is expected to perform better with certain configurations, mainly when using TCP/IP over Ethernet. We tested the four algorithms on terascale Linux clusters DeepComp 6800 and DAWNING 4000A using TCP/IP over fast Ethernet. Results show that our neighbor exchange algorithm performs the best for long messages, the ring algorithm performs the best for medium-size messages and the recursive doubling algorithm performs the best for short messages